The drought in southwestern North America, which lasted from 2000 to 2018, is one of the worst in the region over the past 1200 years, according to a new study.
Reconstructions of the past climate, based on tree trunks' growth rings, revealed only one dry period at the end of the 16th century, which lasted 19 years. The researchers say the recent drought was 47% stronger as a result of anthropogenic climate change.
By studying tree rings in 1,586 sites in the western United States and northwestern Mexico, hydroclimatologist Park Williams of Columbia University and his colleagues have created an 800-year history of the region's climate.
According to Williams, a particularly devastating drought that lasted from about 1575 to 1593 is recorded in historical records and is visible in tree ring reconstructions. The drought may have contributed to the spread of disease among the local population, which infected them with the Spanish conquistadors.
By studying tree rings like this pine cut north of Tucson, Arizona, the researchers determined that the 2000-2018 drought in southwestern North America was one of the worst in 1200 years.
One of the factors controlling precipitation in southwestern North America is the Southern Oscillation, in which fluctuations in surface water temperature in the equatorial Pacific can alter weather patterns in the region. The lower surface temperatures of the Pacific Ocean create atmospheric waves that block Pacific storms and prevent them from reaching southwestern North America, reducing rainfall.
2019 was a year of respite for the region. The same rainy year was observed in the 16th century. But in 2020, the drought returned.